Electrical resistor device



Aug. 15, 1944. s. RUBEN ELECTRICAL RESISTOR DEVICE Filed Sept. 7. 1940 ENV E NTO R awwz! Ha BY ATTORNEY Patented Aug. 15, 1944 UNITED STATES rarrzrrr OFFICE 2,355,680 v ELECTRICAL RESISTOR DEVICE Samuel Ruben, NewRochelle, N. Y.

Application September 7, 1940, Serial No. 355,765

(Cl. fill-6'7) Claims.

This invention relates to an electrical resistor device, and more particularly it relates to an electrical resistor comprising a refractory metal member coated with an insulating coating.

An object of the invention is the provision of an electric resistor comprising an electrical resistance element coated with an electro-deposited substantially inorganic material which is electrically non-conductive and thermally conductive, intimately contacting with it.

A further object of the invention is the provision of an electrical resistor adapted to operate at high temperatures.

Another object of the invention is to provide a wire wound resistor in which the insulating coating upon the wire is highly refractory so as to permit the turns of the resistor to be closely wound together without spacing and to permit multi-layer construction Another object is the provision of an electric resistor of very long life.

Another object is the provision of an electric heater of almost unlimited durability.

Another object is the provision of an electric resistor that is highly efficient.

Another object is the provision of an electric resistor that has a negligible temperature gradient between its heater element and the surrounding and intimately contacting conducting body to he heated.

Another object is the provision of an electrical resistor, the heating element of which is directly wound upon a thermally conductive support with no insulation other than the electro-deposited refractory coating upon the surface of the heating element, and in a permanent position within and in close contact with a thermally conducting material having a lower melting temperature than that of the refractory coating of the heating element.

Another object is the provision of an electric.

the heater element and the material within which it is cast.

Another object of the invention is the provi sion of an electrical resistance element containing a minimum of organic material and which is externally sealed by an intimately applied sheath of metal.

Another object is the provision of an electrical resistance element formed upon a refractory metal base on which is deposited integral therewith a substantially inorganic insulation coating.

A further object is the provision of an electrical resistance element such as described immediacely above in which the insulated refractory element is sealed by a sheath of metal in direct contact therewith.

Other objects of the invention will be apparent from the following description and accompanying drawing taken in connection with the appended claims.

The invention comprises the features of con struction, combination of elements, arrangement of parts, and methods of manufacture and operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the drawing.

in the drawing:

Figure l is a side elevation, partly in section, of a multi-layer resistance element made according to the invention.

Figure 2 is a perspective view of the element;

Figure 3 is a longitudinal section through a modified element;

Figure 4 is a section through another modifica-.

tion; and

Figure 5 is a view of a section of coated resistance wire with part of the coating removed;

Figure 6 is a section through another modification of the invention.

The invention may be said to.comprise an electrical resistor adapted to operate at high temperature utilizing a wound coil of resistance wire having over substantially its entire surface a thin, hard, round, uniform, adherent coating of high heat resistant oxides orv silicates and containing a relatively small amount of organic binder insufllcient to render the coating conduc tive at temperatures beyond the carbonization point of the binder but being present in an amount sufficient to afford flexibility to the coating for the purposes of this invention. In the construction of the resistor the insulated wire is u'nseparated between turns of the coil. Preferably the resistor is in the form of a refractory wire having an electrodeposited insulating coating, as suggested in my co-pending application bearing Serial Number 67,599, which has been wound upon a highly conductive base, such as copper. The metal shield is preferably provided by casting a metal, for instance, an aluminum aly, directly on and around the wound resistance element, and which must have a melting temperature below that of the coating. Likewise the sheath may be added by compressing about the resistance element a sintered metal. And where the use of high temperatures is not essential the sheath or casing may be cl 9. material other than metal, such as cement or vitreous enamel and it need not be in contact with the heating element.

In one form this invention employs a resistance wire, such as that commercially known as mom-cine" or small diameter upon which is coated the electrically insulating and heat reiractory material as described in my co-pending application filed in the United States Patent Ofllce and bearing Serial Number 67,599, filed March 7, 1936.

Heretofore it has been almost impossible to apply a refractory insulating coating of suflicient mechanical strength and thickness to small diameter wires, such as resistance wires in the order of .2 mil diameter. Inasmuch as this type of wire is used in considerable quantity in the manufacture oi electrical resistances, etc., it is highly desirable that an insulating coating capable of withstanding the heat generated by such resistance wires should be provided between turns of such wire, especially where multi-layer resistance units are employed.

I have found that ii shellac be'dissolved and reacted with ammonia to form a water soluble material dilutable to any noticeable degree without precipitation it constitutes an electrolyte solution which serves as a useful medium for suspension oi insulating materials having proper specific gravity, size and structure to enable it to stay in this medium. For the insulating medium I have found that the preferable material should be as nearl as possible in a colloidal condition; a practical electro-depcsitable material is Kaolinite, a colloidal i'onn of kaolin (aluminum silicate).

If a potential is applied between the electrodes in such a solution or mixture a coating will be 45 deposited on the anode in a uniform layer over the part oi the anode contacted by the solution, proportional in thickness to current density and time oi application of current to the electrodes.

The layer will consist of a finely grained deposit plus some water insoluble shellac. After the layer or coating has been deposited it should be dried and baked at a suitable temperature to discharge any water or free ammonia, a touch, adherent coating being so produced.

A typical coating consisting of 200 grains of garnet shellac is dissolved and combined with 1000 c. c. of a 10% ammonia solution which is stirred and heated to 90 C. to completely dissolve the shellac and eliminate any excess or free ammonia. This is first diluted with 3500 c. c. of water and 1125 grains of Haolinlte is added. The material is ball-milled for ten hours.

In applying the insulating layer I prefer a continuous process as described in my said prior application, by which the wire is passed through the electro-depositing solution and thereafter through an oven which de-hydrates and bakes on the de-hydrated material. By a machine in use the wire is passed through the solution four times, being baked between each immersion, whichprovides a non-porous coating. There is a self healing action in the repeated passes to cover any weak or porous areas from the previous pass.

tively, the solution container being negative. If the wire is not charged positively, or if it is negatively charged, and also it alternating current is applied, no coating is deposited.

The potential diilerence between the wire and the metal container in which the solution is held may be about six volts, varying of course with the speed of wire travel through the solution, the

concentration of colloid, the size of wire and the desired surface and potential strength desired. The baking temperature is about 225 C. The addition 01 50 grams of pure white soap to the solution aids in preventing coagulation and gives a longer life to the solution.

It appears that the shellac solution is effective in the electro-depositlon because the shellac, being laccaic acid combines with the ammonium hydroxide to form a water-soluble and electro-decomposible solution which, on electrolysis releases laccaic acid to the anode, the acid being insoluble in the solution. If the coated wire is to be used as a heating element in a heater, it is wound upon a metal carrier, such as a copper rod, and a layer of a molten metal of good thermal conductivity, such as azlnc alloy, is cast about the heater element, or a like material which is slntered, is compressed about the heating element, thus closely contacting with and entirely encasing the heating element.

By the process of my invention described in my said prior application I have been able to produce a flexible yet highly refractory coating derived and electro-deposlted with a colloidal aluminum silicate solution. Such a coating has been found to withstand temperatures of 800 C. and several hundred volts per mil thickness without leakage.

In the prior art when the resistor elements were to be encased, the wire was covered with such a thermal insulator as an asbestos sheet or it was placed between mica plates or covered with a heat insulating cement layer. These methods inherently involve a high temperature gradient between the resistor or heat element and the external or working surface.

The resistor wire used in the devices of my invention can be or unusually small diameter because of the close contact between the resistor coating and the metal cast or compressed about it, as well as the internal pressure and the shrinkage of the encasing metal. For application to some heating devices for household use I have found the nickel-chromium or nichrome wire of about 2 mil thickness to be adequate. Wire coated by this process is flexible, and with its closely adherent coating, can be wound in multi-' layers at high speeds without abrasion or cracking. For the protection of terminals of the heating elements extending beyond the encaslng metal, short tubes of sintemd magnesium oxide are used.

Because of intimate contact between the thinly coated heater element and the ensuing body and the metal body upon which it is wound the power required to raise the temperature oi the heater body to a required degree is relatively lower; overheating does not occur due to the low temperature gradient between the heating element and the working surfaces. Further, the high thermal conductivity oi the elements or the system assists in bringing the body quickly to the desired heat, and if properly designed burning out or overheating is practically impossible under all atmosphere conditions.

In the devices 'of the prior art the heating element must be operated at a temperature much During the process the wire must be charged posiin excess or that employed at the external workpoor thermal contacts prevent heating that is uniform over the working surfaces.

An advantage of the highest practical importance which resistors of this invention possess over resistors of the present commercial art is the close winding of the insulated wire without spacing between turns. As compared either with space wound resistors or resistors employing asbestos insulation, the present device provides either a greater wattage in the same space or by the use of heavier wire a device which will have a comparable wattage output and operate at considerably lower temperatures.

In the devices of the prior art where multilayers of the resistor wire is used, it is necessary to provied thermal and electrical insulation between the layers, which in addition to retarding the transmission of heat from the inner layers, causes a large temperature gradient and excessive volumes for a given power dissipation. By winding the resistor wires in multi-layers without the addition of layer spacers and by directly casting or compressing the encasing cast or sintered metal upon the multi-layer structure the heaters of my invention, through thus minimizing the loss of heat at areas where heat is not desired, produce the desirable result with maximum efliciency.

Under the terms of my invention it is possible to wind the heating members directly upon material of high thermal conductivity, such as copper, which permits rapid internal heat dissipation, or the supporting member may be one of low thermal conductivity.

A factor contributing to making it possible to wind in multi-layers and to avoid variations in the resistance values is the fact that after being encased in the hot metal casting or the sintered metal body, such as aluminum or zinc or the alloys, the carbon or organic material content of the insulation is of such a minimum value that leakage or breakdown, due to carbonization does not occur.

Referring to the drawing:

Figures 1 and 2 show a fixed resistor for use in general circuit applications. This comprises a spool or form l3 of insulating material such as porcelain, lavite, izolantite, sillimanite or the like. The coated wire I is wound without spacing between turns on form l3 inv mult-layer fashion without the interposition of any extra insulating layers and the ends are scraped clean of coating material and electrically connected to terminal rivets l4 and I5, respectively, which pass through-theend flanges of form IS, the electrical connection being made by a mechanical riveting operation or by welding. A pair 01' terminal lugs l6 and H are secured to the ends of form l3 by the respective rivets and-form the electric terminals of the element.

If greater rigidity and higher abrasive resistance aredesired in the flnishedfelement they can be'obtained by applying a glazing material prior to any of the above heat treatments. For example, the wound element, before heating, can be sprayed, dipped or painted with a. hydrolyzed ethylsilicate solution, preferably with finely divided Kaolinite and talc suspended therein. A

suitable mixture consists of 50% Kaolinite and 50%v talc added to an equal weight of hydrolyzed ethyl silicate. This glazing layer gives the coating a smooth surface and bonds adjacent turns of the winding together into a rigid integral unit.

Upon heat treatment the organic ethyl "silicate is decomposed leaving a silica binder. Methyl or glycol silicate can be substituted for ethyl silicate.

Likewise a water solution of sodium silicate may be applied'if high voltages are not encountered. The best glazing effects can be obtained by heating at least to 1000 C.

The element of Figures 1 and 2 may be covered and protected by a metal sleeve 18 of aluminum or other metal which fits over the flanges on form l3 and has its ends spun down over the ends of the form thereby completely enclosing the winding Ill. A pair of lugs I9 and 20 secured to sleeve 18 serve as mounting means for the element.

Figure 3 shows an element of different shape, the coated wire M in this case being wound without spacing between turnson a shorter insulator form or spool 21, the wire being connected to terminal lugs 22 and 23. A metal sleeve 24, fits over spool 2|, and is spun down over its ends. This form is adapted to be mounted on a bolt passing through central hole 25 in spool 2 I.

Figure 4 shows an element having a cast metal sheath. In this case the coated wirelll is woundwithout spacing between turns, or an insulating form 26 having a large diameter flange 2'! at one end and a small diameter flange 28 at the other. The wire is connected to rivets 29 and 30 whose heads are countersunk in the inner face of flange 21. The countersunk bores are filled with alundum cement after the wires are attached to insulate the connections. 3i and 32 are held by rivets 29 and 30 on the end of form 26. A metal sheath 33 is cast over the winding after the element has been heated .as described to eliminate organic material. This may be done by placing the wound element into a mold and casting the metal about it. The metal sheath may be made flush with the outer edge of flange 21 as shown. The metal is cast directly against the coated wire winding. Due

to the prior elimination of the volatile organic material the casting will be free of blow holes.

A suitable alloy for the cast sheath where low temperatures only are to be encountered consists so of:

1 Per cent Aluminum 4.1 Magnesium .1 Copper 2.7

*Zinc 93.1

which alloy melts at about 390 C. For higher temperatures I prefer an alloy containing approximately 98% aluminum and having a melting point in the order of 650 C. Other metals and "alloys, such as copper alloys, can be used where still higher temperatures are to be met or where other properties such as higher conductivity are desired. a Figure 6 shows a resistor somewhat similar to the one shown in Figure 4. In the unit illustrated, the coated wire I'D is wound in multilayer form on'an aluminum spool having small diameter flange 34 at one end and a larger diameter flange 42 at the other end. The wire is connected to screws 35 and 38 extending through and insulated from the spool by insulating members 36 and terminals are provided by lugs 39 and 40 held in place by nuts 35 and 38- and insulated from the spool by washers 31. If de- A pair of terminal lugs sired, the unit can be constructed in plug-in form, prongs being substituted for the terminals shown. An aluminum sheath 4! has been cast directly over the winding to protect the unit and to afford a rapid heat transference. This heat transference may be further improved and the unit can be made capable of dissipating higher wattage by etching or otherwise roughening the outer surface of the casting and also by blackening the casting.

For the finely divided refractory inorganic insulating materials used in the coating I prefer a mixture of Kaolinlte and talc. However, other very finely divided high heat resistant oxides and silicates may be used although with. not as satisfactory results. Among such materials may be mentioned chromium oxide, beryllium oxide, titanium oxide, ievigated aluminum oxide, etc.; where such materials are used it is desirable that they be ground down to four hundred mesh size.

As the organic binder material I prefer shellac. However, it is possible to substitute other drganic materials such as rosin, hydrogenated -rosin,

latex, hydrogenated polymerized turpentine, guin arabic, gum tragacanth. In the electro-deposition process used in making the insulated resistance wire in this invention, however, shellac is the most desirable material. Preferably the amount of organic binder should be within the limits of 5% to 36%, dependent upon the temperature rise to be encountered. Where one or two mil diameter wires are coated the preferred amount of shellacis in the order of This application is a continuation in part of my co-pending applications bearing Serial Numbers 127,101, filed Feb. 23, 1937 (now Patent No. 2,213,969, issued Sept. 10, 1940); and 288,810, filed Aug, 12, 1939 (now Patent No. 2,327,462, issued Aug. 24, 1943).

Having described my invention what I claim as new and desire to secure by Letters Patent is:

1. An electrical resistor adapted to operate at high temperatures comprising a wound coil of refractory metal resistance wire, said wire having over substantially its entire surface a thin, hard, round uniform substantially non-softening adherent coating of inorganic insulating material of the high heat resistant silicates and oxides time. said coating being heat bonded to the surface of said wire, said coating containing a relatively small amount of insulating organic binder, at least in the order of 5%, but insuflicient to render said coating conductive at temperatures beyond the carbonization point of said organic binder, said insulated wire being flexible and bendable, said insulated wire being unseparated between the turns of the coil.

refractory metal resistance wire, said wire having over substantially its entire surface a thin, hard, round uniform substantially non-softening adherent coating of inorganic insulating material such as Kaolinite, said coating being heat bonded to the surface of said wire, said coating containing a relatively small amount of insulating organic binder, at least in the order of 5%, but insufficient to render said coating conductive at temperatures beyond the carbonizatlon point of said organic binder, said insulated wire being flexible and bendable said insulated wire being unseparated between the turns of the coil.

4. An electrical resistor adapted to operate at high temperatures comprising a wound coil of refractory metal resistance wire, said wire having over substantially its entire surface a thin, hard, round uniform substantially non-softening adherent coating of inorganic insulating material of the high heat resistant silicates and oxides type, said coating being heat bonded to the surface of said wire, said coating containing a relatively small amount of insulating organic binder, at least in the order of 5%, but insufficient to render said coating conductive at temperatures beyond the carbonization point of said organic binder, said insulated wire being flexible and bendable, said insulated wire being unseparated between the turns of the coil, said resistor being substantially completely sealed by metal cast directly on the insulated wire.

5. As an article of manufacture, a flexible high temperature electrical heating element comprising a wire of refractory metal having bonded thereto a thin, hard and adherent flexible insulating coating of uniform thickness, said coating comprising finely divided aluminum silicate of the Kaolinite type and an organic resin, said resin being dissolvable in an aqueous alkaline solution, said resin being present in a relatively small amount insufficient to render said coating conductive at temperatures beyond the carbonizetion point of said resin but being present in an amount suflicient to afford flexibility to said coating, said coating being hard, adherent and nonconductlve at temperatures above the carbonization temperature of said resin.

6. As an article of manufacture an easily bendable electrical heating element comprising a wire of refractory metal having a flexible coating of finely divided aluminum silicate of the Kaolinite type and an organic resin formed in situ thereon, said resin being dissolvable in an aqueous alkalinc solution, said coating being continuous,

2. An electrical resistor adapted to operateat high temperatures comprising a wound coil of refractory metal resistance wire, said wire having over substantially its entire surface a thin, hard,

round uniform substantially non-softening adherent coating of inorganic insulating material of the high heat resistant silicates and oxides solid, impermeable and self-sustaining and so bonded to the wire as to allow said wire to be readily collable, said resin being present in said coating in a relatively small proportion, sufficient to afford flexibility to said coating but insuflicient to render said coating conductive when the heater is operated at temperatures in excess of the carbonizatlon temperature of said resin.

7. As an article of manufacture, an electrical resistance wire having bonded theretoa thin,

hard and adherent, flexible insulating coating of uniform thickness, said coating comprising inorganic insulating material of the high heat resistant silicates and oxides type and containing a non-vaporizable insulating organic binder, said coating being continuous, solid, and impermeable and so bonded to the wire as to allow said wire to be readily coilable, said binder being present in said coating in a sumcient amount to aiford flexibility thereto but insumclent to render said coating conductive when heated to temperatures in asuaeso excess of the carbonization temperature of said organic binder. v

8. As an article of manufacture; an electrical resistance wire of small diameter having bonded thereto a thin, hard and adherent, flexible, electrodeposited insulating coating of uniform thickness, said coatingcomprising inorganic insulating material of the high heat resistant silicates and oxides type and containing a non-vaporizable insulating organic binder, said coating being continuous, solid, and impermeable and so bonded by heat to the wire as to allow said wire to be readily coilable, said binder being present in said coating in a sufilclent amount to aflord flexibility thereto but insuiiicient to render said coatin conductive when heated to temperatures in excess of the carbonization temperature 01 said organic binder.

9. As an-article of manufacture, an electrical resistance wire of small diameter having bonded thereto a thin, hard and adherent, flexible, electrodeposited insulating coating of uniform thickness, said coating comprising aluminum silicate and containing a non-vaporizable insulating organic binder, said coating being continuous, solid, and impermeable and so bonded by heat to the wire as to allow said wire to be readily coilable, said binder being present in said coating in a suiiicient amount to aflord flexibility thereto but insuiiicient to render said coating conductive when heated to temperatures in excess of the carbonization temperature of said organic binder.

10. As an article oi manufacture, an electrical resistance wire of small diameter having bonded thereto a thin, hard and adherent, flexible, electrodeposited insulating coating of uniform thickness, said coating comprising aluminum silicate and talc and containing a non-vaporizable insulating organic binder, said coating being continuous, solid, and impermeable and so bonded by heat to the wire as to allow said wire to be readily collable, said binder being present in said coating in a sufficient amount to afiord flexibility thereto but insuflicient to render said coating conductive when heated to temperatures in excess of the carbonization temperature of said organic binder.

SAMUEL RUBEN. 

